In this photo provided by the Las Vegas News Bureau, Rihanna takes the stage during her "Rihanna Diamonds World Tour" at the Mandalay Bay Events Center on the Las Vegas Strip on Friday, April 12, 2013. (AP Photo/Las Vegas News Bureau, Glenn Pinkerton)

Rihanna has postponed tonight's Toyota Center appearance in Houston due to illness, according to a statement issued by Live Nation, the show's promoter. Her Diamonds World Tour is expected to continue Tuesday in Dallas. The tour, which began last month, went off without a hitch Friday night in Las Vegas.

The promoter urges fans to hold onto their tickets for a rescheduled date to be determined. However, refunds are available, but tickets must be taken to Toyota Center, even if they were bought at another outlet.